Ping-pong handover is a term that can be used to describe a scenario where a user equipment in a cellular radio network is changing back and forth between the same pair of cells for a number of times during a period of time. Ping-pong handover is also sometimes referred to as repeated handover. Ping-pong handovers are considered to be harmful in several ways. First, it causes unnecessary signaling load. Second, it affects the end-user experience significantly, since during handover, the data reception and transmission is halted, some amount of data may be lost, and the “recovery” after a handover may take considerable time especially if the mobile is using high data rate services. Delay sensitive applications can be also harmed significantly, e.g., real-time gaming.
In cellular radio systems handover is typically controlled by evaluating radio measurements performed by the user equipment. If the measurement from a new cell becomes better than the old one, the handover can be initiated. Since measurements fluctuate due to natural reasons, certain thresholds and smoothing are applied. The setting of these thresholds and smoothing parameters can be different and can be subject to optimization of different sorts.
Existing methods for addressing the ping-pong handover problem can typically be described as two steps:                In the first step the ping-pong is detected by looking at historical handovers        In the second step parameters including thresholds, penalty time etc. are adjusted.        
The existing methods of solving a Ping-pong handover problem typically look at the observable statistics and try to reduce the number of ping-pongs. For example, in WO2009021711, a method involving transmission of system messages between the mobile radio stations and the base stations is described. The system messages for initiating the handover are used to transmit historical information relating to handovers which have already been performed. The information is used automatically to ascertain and set optimum operating parameters for the mobile radio stations or one of the base stations which are involved. In EP2073578, a priority level is assigned for each handover trigger cause. The coded causes are sub-divided into unrestricted handover class of highest priority and restricted handover class of high or normal priority. A Handover request is not issued if an identifier of the target base station is the same as the stored identifier and a penalty elapsed time is below configured value, when the trigger condition of an incoming handover belongs to a restricted class. In WO2009031108, a method is described involving handing over a user equipment from a first network access node to a second network access node and not considering the first network access node as a handover candidate from the second network access node for some period of time unless there is indicated a change in channel conditions that exceed a threshold in one or both of time and an amount of change. Also, in WO2009004405, a ping-pong handover avoiding method is described that involves deciding on allowing or preventing an intended handover based on the result of comparison between the decision criteria of the intended handover and the decision criteria of previous handovers of a mobile station to a base station.
However, as exemplified by the above methods, existing solutions also provides limitations on handover, which can prevent an optimal handover between cells. Thus, in existing solutions upon detecting a ping-pong handover, the handover decision becomes more and more conservative (as a result of an increase some thresholds). Consequently, the probability of failed handover or unprepared handover increases. This is a trade-off to which there exists no good solution. Hence, there is a need to provide methods and devices for reducing ping-pong handover that reduces or eliminates an increased risk of failed handover or unprepared handovers.